PROJECT SUMMARY/ABSTRACT Aging is the primary risk factor for the majority of chronic diseases. Studies in mice have implicated specific growth and differentiation factors (GDFs) and proteins secreted by senescent cells as potential modifiers of aging. The objective of this proposal is to establish the rationale and provide robust clinical evidence for GDF8, GDF11, and senescence-related proteins eotaxin (CCL11), intracellular adhesion molecule 1 (ICAM1), activin A (AA), and plasminogen activator inhibitor 2 (PAI2), as indicators of biological age and age-related conditions in humans. The central hypothesis is that circulating concentrations of GDFs and senescence-related proteins are associated with, and predictive of, clinically important health outcomes and can be altered by physical activity. Samples from the Lifestyle Interventions and Independence for Elders (LIFE) Study; the largest and longest randomized trial of a physical activity intervention in older adults, will be used to test this hypothesis, and samples from the Health, Aging, and Body Composition (HABC) Study will be used to validate study findings. A novel multiplexed liquid chromatography-tandem mass spectrometry assay will be leveraged to accurately quantify GDFs, and an advanced multiplexing platform will be used to measure senescence-related proteins in LIFE and HABC biospecimens. In Specific Aim 1, a multidisciplinary team will first determine the extent to which baseline concentrations of GDF8, GDF11, CCL11, ICAM1, AA and PAI2 are associated with baseline measures of physical (i.e., gait speed, Short Physical Performance Battery (SPPB) score), cardiopulmonary (i.e., blood pressure, forced expiratory volume), and cognitive (i.e., processing speed, memory) function, inflammation, and prevalence of multimorbidity (based on the ICD-9 codes for 20 chronic conditions). In Specific Aim 2, the degree to which baseline concentrations of GDFs and senescence-related proteins predict longitudinal changes in a) gait speed and SPPB score, b) major mobility disability (i.e., the inability to walk 400m), c) combined cardiovascular events (e.g., myocardial infarction, heart failure, stroke); d) adjudicated falls and injurious falls, e) cognitive function (as Aim 1), and f) the number of chronic conditions (as in Aim 1), at 1 and 2 years in LIFE and at 2 and 4 years in HABC will be determined. Finally, Specific Aim 3 will address whether a structured physical activity intervention impacts longitudinal changes in GDF8, GDF11, CCL11, ICAM1, AA, and PAI2, compared to a health education control intervention, and the degree to which change in the concentrations of these proteins parallel change in the health outcomes described in Aim 2. The successful completion of the proposed research will fill an important translational gap in our understanding of how GDFs and senescence-related proteins predict and, therefore, potentially mediate aging related disability and disease in older women and men. Ultimately, these proteins may be viable targets for innovative therapies to extend human healthspan.